Lesson 2

Types

  • int a whole number

  • str a list of characters

  • float a floating-point (decimal) number

  • bool a boolean value True or False

  • Window the application window that draws graphics

  • Sprite a rectangular image we can manipulate in the window

  • Color the red, green, and blue values that describe a color

Use the type() function to see an object’s type.

Remember:

  • function arguments have specific types.

  • properties (member variables) of a class have specific types.

  • function return values have a specific type.

Questions:

What is the function input() ‘s return value type? What is the type of the x and y properties of a Sprite?

Type Conversion

Implicit Conversion

x = 3
y = .14
z = x + y
print(z)

Explicit Conversion

x = '3'
y = .14
z = float(x) + y
print(z)

x = '3'
y = .14
z = x + str(y)
print(z)

Classes

We can create custom types by defining a class. A class defines properties and methods or modifies the properties and methods of an existing class through inheritance.

For example, we can create a class that inherits from the Sprite class that includes all the properties and methods of a Sprite, plus any additional properties of methods we define. We can also set the specific properties so that all class instances share the same data.

class Elephant(Sprite):

   def on_create(self):
      self.image = 'elephant.png'

A class is similar to a blueprint or a plan. Just like a house is built from a blueprint, an object is created from a class definition. In pycat, we use the window object to create a new object of type Elephant.

elephant = window.create_sprite(Elephant)

Loops

for i in range(10)
   print(i)